1. Field of the Invention
The present invention relates to a motor drive system for driving a motor provided with a plurality of windings.
2. Description of the Related Art
In the case of drive controlling a large motor with high torque and huge power by an inverter device (servo amplifier), a large capacity inverter device is required. However, because there are limitations in regards to the elements constituting the inverter device, it is difficult to configure one inverter device which controls a large motor. Therefore, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2005-86918, in general, a plurality of small capacity inverter devices which are connected in parallel are used as an alternative.
FIG. 4 shows a block diagram of one of the conventional motor drive systems as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2005-86918. The motor drive system 100 shown in FIG. 4 mainly comprises a large motor 110 provided with a plurality of windings, a motor position detector 120 for detecting a position of a rotor of the motor 110, and an amplifier group 140 including a plurality of amplifiers 200a to 200n which are linked together with each other. Further, the amplifiers 200a to 200n include respective inverters 210a to 210n. 
As shown in the figure, the motor 110 is connected to each of the amplifiers 200a to 200n by power line cables 400a to 400n. Further, a position feedback cable 410 extending from the motor position detector 120 is branched in midstream and connected to all of the amplifiers 200a to 200n. 
In addition, the motor drive system 100 includes a numerical control device 130. In the numerical control device 130, axis position commands of the motor 110 generated by a main processor 300 are input to the axis control parts 310a to 310n. The axis control parts 310a to 310n generate PWM (pulse width modulation) commands (voltage commands) and supply the commands to one amplifier 200a through a serial bus control circuit 320 and a serial communication cable 420. Because the amplifiers 200a to 200n are mutually connected, the inverters 210a to 210n of the respective amplifiers 200a to 200n drive the motor 110 based on the PWM commands.
However, as shown in FIG. 4, when a single motor 110 is driven, only a single rotor position detection signal can be obtained. Therefore, in the prior arts, in order to supply the single rotor position detection signal to all of the amplifiers 200a to 200n, the position feedback cable 410 must be branched to all of the amplifiers 200a to 200n. The wiring operation of this kind of position feedback cable 410 is complicated, requires a large effort and time, and is costly.
Further, FIG. 5 shows a block diagram showing another conventional motor drive system. The motor drive system 100′ shown in FIG. 5 is different from the motor drive system 100 shown in FIG. 4 in the point that the axis control parts 310a to 310n are included in the respective amplifiers 200a to 200n. Even in the motor drive system 100′ shown in FIG. 5, only a single rotor position detection signal can be obtained. Thus, similar to the aforementioned system, the position feedback cable 410 must be branched to all the amplifiers 200a to 200n. 
The present invention has been created considering the above drawbacks, and an object of the present invention is to provide a motor drive system capable of driving a large capacity motor by a plurality of inverter parts without complicating the configuration.